Investigating the Trap-State Emission of CdTe Nanoplatelets

Recently, two-dimensional II-VI semiconductor nanoplatelets (NPLs) have gained tremendous attention due to their exceptional photophysical properties including sharp emission spectra, tunable absorption and emission, large absorption cross section and giant oscillator strength etc. With the advancement of synthetic strategies, these NPLs now can be synthesized with controlled thickness even down to atomic precision. But while most of the progresses have been made with CdSe NPLs, the controlled synthesis of CdTe NPLs still remains challenging; even the detailed photophysics involving them remain unexplored. Here in this work we aim to synthesize CdTe NPLs with controlled thickness and decipher their carrier dynamics in single particle and ensemble level. With this aim we synthesized three monolayer NPLs which interestingly show a distinct excitonic emission and a broad emission band which can be related to trap states emission. The time resolved photoluminescence study reveal two distinct PL decay behavior when monitored at different probe wavelengths. The prolonged PL decay (>30ns) of the broad emission also suggests that it is related to trap emission. To dig deep into the mechanistic pathways of the photogenerated charge carriers, temperature dependent photoluminescence, single particle photoluminescence imaging and ultrafast pump-probe measurements are employed. Understanding the trap states nature will help us to find a key to manipulate them and these long lived trap states carriers can be utilized for their potential applications such as in photocatalysis.